1. Field of the Invention
The invention is directed to optical communication systems in general and, more particularly, to bidirectional optical networks that include two or more bidirectional waveguides each transporting counter-propagating WDM optical signals and having a data bridge for directing selected bit streams encoded on one optical channel from one bidirectional waveguide to plural channels on another bidirectional waveguide.
2. Description of the Related Art
As the need for communication signal bandwidth increases, wavelength division multiplexing (WDM) has progressively gained popularity for multiplying the transmission capacity of a single optical fiber. A review of optical networks, including WDM networks, can be found in Ramaswami et al., Optical Networks: A Practical Perspective (Morgan Kaufman, (copyright) 1998), the disclosure of which is incorporated herein by reference. Typically, wavelength division multiplexed optical communication systems have been designed and deployed in the long-haul, interexchange carrier realm. In these long-haul optical systems, a wavelength division multiplexed optical communication signal comprising plural optical channels at different wavelengths travels in a single direction on a single fiber (unidirectional transmission). Because the communication traffic in such systems commonly travels many hundreds of kilometers, the need for add-drop multiplexing of individual channels is infrequent (if at all), occurring at widely-spaced add-drop nodes.
Although the optical infrastructure of long-haul WDM optical systems can accommodate future traffic needs created by increased demand from traditional and multimedia Internet services, this traffic must first be collected and distributed by local networks. Currently, such local networks are predominantly structured to carry a single wavelength, time-division multiplexed (TDM) optical signal along a fiber network organized into various ring structures. To route the various components of the TDM signal, numerous electronic add-drop multiplexers are positioned along the fiber network. At each add-drop location, the entire optical signal is converted into an electrical signal; the portions of the electrical signal which are destined for that add-drop point are routed accordingly. The remaining portions of the electrical signal are converted back to a new TDM optical signal and are output through the electronic add-drop multiplexer. Thus, before a user can access the bandwidth-rich WDM long-haul transport networks, he must first pass through the bottleneck of the local networks.
Although unidirectional WDM optical systems are suitable for conventional long-haul interexchange carrier markets, metropolitan (local) communications systems require extensive routing and switching of traffic among various nodes positioned within interconnecting optical fiber rings. Consequently, smaller metropolitan markets require considerably more extensive add-drop multiplexing in order to successfully implement wavelength division multiplexing in their short-range systems. Further, in order to maximize the effectiveness of wavelength division multiplexing in these local areas, it would be useful to implement bidirectional WDM optical systems, e.g., to enhance network design flexibility. In a bidirectional WDM system counter-propagating WDM optical signals, each of which carry a number of optical channels, are carried on the same waveguiding medium, such as a single optical fiber. Implementation of a bidirectional system requires several considerations not present in the conventional unidirectional optical systems. Add-drop multiplexing in a bidirectional optical environment becomes considerably more complex since optical channels are usually selected from each of the counter-propagating WDM optical signals. In addition to the difficulties posed by add-drop multiplexing channels from two counter-propagating WDM optical signals, there must also be techniques for directing channels from one bidirectional WDM optical waveguide to another. For example, in a local metropolitan network, it would be desirable to optically transfer traffic among adjacent bidirectional rings.
In U.S. patent application Ser. No. 09/704,566 entitled xe2x80x9cBidirectional WDM Optical Communication Network With Optical Bridge Between Bidirectional Waveguides,xe2x80x9d assigned to the assignee of the present invention, the disclosure of which is incorporated by reference herein, a technique is proposed which permits the transfer of an optical channel from one bidirectional WDM optical system to another bidirectional WDM optical system. While this application provides a useful technique for the routing of an entire optical channel between bidirectional optical systems, it does not provide a technique for taking portions of the information encoded on an optical channel carried by one bidirectional system and dividing it among plural optical channels carried on another bidirectional optical waveguide. There is a need in the art for a data bridge which would permit such data routing from a channel carried by one bidirectional optical waveguide to plural channels carried by another bidirectional optical waveguide. Such a device would permit effective implementation of bidirectional wavelength division multiplexing in local, metropolitan markets requiring high volumes of signal re-routing and allow creation of flexible network topologies.
The present invention relates to a bidirectional optical network including a bridge for selectively transferring information from an optical channel carried on a first bidirectional wavelength division multiplexed optical waveguide to at least two optical channels on a second bidirectional wavelength division multiplexed optical waveguide. The network includes a first bidirectional optical waveguide carrying a first bidirectional WDM optical communication signal which includes a first WDM signal having plural first optical channels propagating in a first direction and a counter-propagating second WDM signal including plural second optical channels.
The network also includes a second bidirectional optical waveguide carrying a second bidirectional WDM signal which includes a third WDM signal composed of third optical channels and a counter-propagating fourth WDM signal having plural fourth optical channels.
A bridge is interposed between the first and second bidirectional optical waveguides. The bridge includes a first optical add-drop multiplexer optically communicating with the first bidirectional waveguide which selects at least one optical channel from the first WDM signal. The first optical channel carries a first series of data bits and a second series of data bits encoded on the optical channel.
The bridge also includes a first optical network interface which includes an optical to electrical conversion element for converting the selected first optical channel to a first electrical signal which includes the first and second series of data bits. The optical network interface separates the first series of data bits from the second series of data bits and encodes a second electrical signal with the first series of data bits and encodes a third electrical signal with the second series of data bits. Alternatively, the first and second series of data bits could have been placed on separate electrical signals by the optical to electrical conversion element.
The electrical signals respectively encoded with the first and second series of data bits electrically communicate with a second optical network interface. The second optical network interface includes at least two electrical to optical conversion elements such that the second electrical signal encoded with the first series of data bits is used to modulate a second optical channel and the third electrical signal encoded with the second series of data bits is used to modulate a third optical channel. These optical channels are sent to a second optical add-drop multiplexer optically communicating with the second bidirectional optical waveguide where they are added to the counter-propagating WDM optical signals on the second bidirectional waveguide. An advantageous feature of the present invention is that the two optical channels encoded with the two series of data bits may travel in the same or opposite directions when added to the second bidirectional waveguide, further enhancing network flexibility.